The invention relates to the generation of special video effects and particularly to systems for combining selected percentages of multiple video images into a composite image, as determined by respective key signals.
Various apparatus and techniques exist at present for selectively handling, combining and/or otherwise manipulating one or more video images in television systems. Typical of such apparatus are analog and/or digital schemes for providing a dissolve video output signal wherein, for example, an attenuator network controlled by a counter incrementally changes the signal level of one video input in one direction from a first of opposite level limits while incrementally changing the signal level of a second video input in a corresponding manner, but in the opposite direction from the other of the opposite level limits. Such a scheme provides a uniformly conducted dissolve operation, wherein first video information is replaced by second video information, while a summation of the varying percentage of each of the two video signals ideally always is equal to 100% over the entire dissolve interval. The attenuation signal in such a scheme is operated at a clock rate corresponding to the video field rate, that is, at a rate of one times or a sub-multiple of the vertical sync rate. Such a digitally controlled lap dissolver network is illustrated, by way of example, in U.S. Pat. No. 3,598,908, assigned to the same assignee as is this application.
Production switchers also commonly are used to perform switching and various picture manipulations of video signals in the analog domain. Video signals such as generated by cameras in real time, or by recorders in non-real time, are variously combined, moved and/or otherwise selectively manipulated in such switcher apparatus. Generally in combining video signals, the switcher employs control signals commonly termed chroma key signals which, for example, are used to cut a hole in a background video signal, which hole then is filled with a foreground video signal to provide a composite video image of the two signals. Thus the combined image is formed of portions of either one or the other video signal; that is, switchers generally are capable of handling only foreground and background signals.
As may be seen, the video lap dissolver type of apparatus briefly discussed above, provides simple ramp switching of two video signals, wherein the video signals themselves are gradually switched to replace one with the other. Likewise, the production switchers of previous mention perform a switching operation on the video signals themselves, or on the video paths thereof, in the course of performing a soft or hard switch between the various incoming signals. The above switching techniques in general perform the switching operation in the analog domain and/or perform hard digital switching wherein inputs are either off or on. Thus, in general, prior techniques of combining video signals or images suffer from the problem that stepping motions are visible in the picture during movement of the images, and further that aliasing components become apparent in regions of hard edge transitions. Additionally, such schemes generally do not afford the requisite degree of control repeatability and accuracy presently required in the field of digital special effects.
The increased use of digital special effects in television has created an increasing demand for more sophisticated picture manipulation capability, and improved picture quality, while further requiring added flexibility in human interface with the apparatus than presently is provided by systems such as the dissolve apparatus and/or the production switchers of previous mention. It follows that it is essential that new product designs be developed which provide flexible, easily managed control and signal channel combinations that allow an operator to quickly and simply adapt a system to changing operational needs on a modular basis. Further, in view of the trend towards the all-digital environment of future television systems, any new digital special effects system must be capable of all-digital operation and thus must perform all picture processing operations in the digital domain.
Recently, digital optics special effects systems have been introduced in the television field which modify and manipulate the geometry of video pictures at real time video rates, while operating entirely within the digital domain. One such system allows picture geometry changes on any spatial axis of an inherently two-dimensional video picture, including true three-dimensional perspective, at real time video rates. This latter system is manufactured by Ampex Corporation, Redwood City, Calif., under the name ADO digital special effects system, and is described in the Ampex Digital Optics Service Manual No. 1809550, issued November, 1983. More conventional effects such as picture size and position changes also are produced by the system, but with absolute visual smoothness of picture movements and high picture quality throughout all motion and manipulation of the video pictures. Thus, high quality picture manipulation is performed smoothly at any speed without stepping motions by the picture during movement.
The present invention combination, hereinafter termed a "combiner" for convenience, adds yet a further level of sophistication to existing special effects systems. To this end, the present combiner contemplates an additional manipulation of multiple video images utilizing a video effect or technique known as video channel combine. A "combine" is effected by combining two or more channels of video signals in such a way as to make scenes or images corresponding to the various signals, appear to be one behind the other as in accordance with a selected "priority". For example, a combine may display a first video image from one channel of highest priority in front, followed by a second video image from a second channel, which in turn is in front of and followed by a third video image from a third channel, etc. The combine may appear over a selected background such as black or gray, wherein the background has the lowest priority and fills all display areas where the proportions of the composite video image do not add up to 100%.
Further, the video images of the various channels in a combine may exhibit various degrees of transparency. This allows images with lower priorities, that is, images which would be hidden behind another image, to partially show through; i.e., to be partially visible due to the transparency of the image or images in front. In a further effect, the images of any channel also can be dimmed if desired, to the black, gray or other desired background. The dimming effect is enhanced by a light source feature which highlights selected images or planes while dimming others. The determination of the transparency and dimness of the channels, like the changes in priority of the channels, can be programmed to occur automatically, and are made on a video field-by-field basis.
Thus, the present combiner overcomes various shortcomings in the art discussed above, while providing various combine effects heretofore unavailable in the art. Because timing differences between video channels are completely eliminated, combines produced by the present combiner synchronize together perfectly. Multiple images of more than just a background video signal and a foreground video signal are smoothly combined with a high degree of control repeatability and accuracy. In addition to providing extensive ranges of transparency and intensity, soft edge keying with a minimum of aliasing is accommodated if a soft key is introduced by the signal system. The processes of designating priority, transparency and dimness are more readily achieved by the present combiner, since the system processes the controlling key signals, rather than processing the video images themselves as heretofore commonly done in the art.
As a further advantage, a combiner employing at least four channels can produce two independent combines simultaneously, with each combine being the result of combining two video images from two channels. Any one of the four channels may be selected for combination with any other channel to provide a combine. Each combine process is controlled by one of two different user control panels, while each combine utilizes different pairs of video images of the four video channels.
More particularly, video channel combines are produced by digitally processing binary numbers representing values of video image information in a channel for picture elements of a display. Channels to be combined are first synchronized so that binary numbers representing image values in different channels, arrive at processing logic in the combiner during the same cycle of processing clocks. The binary numbers are combined to produce new binary numbers which represent a combined or composite video image value to be displayed at the same temporal and spatial location of the display of the composite video image. Numbers are combined in the course of processing, by taking a preselected percentage of each number's value and adding the products thereof. Total percentages resulting from the summation of all numbers for each composite video image value, including the number corresponding to the percentage of background desired, is equal to 100%.
By way of illustrating the present combiner configuration, two or more channels of digital video are supplied directly to cutter means by two or more signal systems. The cutter means perform the process of reducing (i.e., "cutting") the binary numbers of previous mention, to some percentage of their original value. Each respective channel also supplies associated boundary key data to respective keyer means which, in turn, supply respective processed key signals indicative of the percentage that the binary numbers of each channel are to be cut. The processed key signals are coupled to the respective cutter means of previous mention. The multiple channels of cut video signals are fed from the cutter means to adder means. The adder means perform a summation, or summations, of the cut video signals and supply one or more outputs therefrom. The outputs correspond to the composite video images formed by one or more combines, processed in accordance with the invention combination. The composite video images are supplied back to the signal system for conversion to a conventional analog composite video signal. The signal system may comprise the ADO system of previous mention.
Accordingly, it may be seen that the present combiner provides for precisely combining a plurality of video images manipulated by the signal system with a selected background. Further, the combiner provides the channel combines without switching the major video paths, or the video signals themselves, as is commonly performed by the prior art signal combining schemes discussed above. In a system having at least four channels, the combiner provides the generation of at least two independent combines simultaneously, employing any combination of two of the four available channels under control of two separate control panels. Thus two independent users may perform independent combines simultaneously, wherein the combines need not be timed to the same reference. In a further feature, a process for automatically determining the priority of the channels, and thus the order of the video images in a combine, on a field-by-field basis, is employed to continuously determine in real time which channel or channels are in front of the other.